<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>15-作业-发送短信</title>
</head>
<body>
    手机号码: <input type="number"> <button>发送验证码</button>
    <script>
        /* 
        需求：
        1. 点击按钮。开启倒计时。按钮禁用
        2. 倒计时结束，按钮恢复
        */
       let btn = document.querySelector('button');
       btn.addEventListener('click',function(){
           let index = 3;
           this.disabled = true;   // 按钮禁用
           btn.innerHTML = index;

           let timer = setInterval(()=>{
               index--;
               btn.innerHTML = index;
               if(index==0){
                   clearInterval(timer);
                   this.disabled = false;
                   this.innerHTML = '发送验证码';
               }
           },1000);
       });
    </script> 
</body>
</html>